Defence secretary Leon Panetta embarked on a five-day trip to the Middle East on Sunday during which he is expected to meet the new leaders of Tunisia and Egypt and hold bilateral talks with long-standing US allies Israel and Jordan.

High on the agenda at each stop is expected to be the accelerating crisis in Syria amid ongoing clashes between government troops and rebels in the strife-torn country.

The visit to Israel will come just days after Republican presidential challenger Mitt Romney tours the country in a politically significant visit, given his past sharp criticism of the White House over its handing of Middle East policy.

Panetta's press secretary, George Little, said the trip is intended to affirm a US commitment to stability in the region at a time when the US military is shifting more of its attention to Asia.

"That will require strengthening traditional alliances with countries like Israel and Jordan and building strong partnerships with new democratic governments," Little said last week in previewing the trip.

The visits to Egypt and Tunisia come as the White House attempts to cultivate new ties between Washington and the emerging Islamist leaders in the two countries.

In Tunis, Panetta plans to meet with his Tunisian counterpart as well as President Moncef Marzouki, leader of the small, secular Congress for the Republic party.

Panetta is scheduled to visit the North Africa American Cemetery near Tunis, resting place for 2,841 US military members killed in the World War II invasion and occupation of Morocco, Algeria and Tunisia in 1942-43.

Among them is army air corps pilot Foy Draper, who won a gold medal in the 1936 Summer Olympics as a member of the U.S. 400 meter relay team. He was killed on a mission over Tunisia in January 1943.

During his visit to Jerusalem, Panetta is expected to highlight cooperation with Israel on building more effective missile defences, including the Iron Dome system that is designed to shoot down short-range rockets and artillery shells.

The US has provided $205m for the project, and on Friday, Obama announced the release of a further $70m.